Trailer disconnected in dash.

So I bought a trailer that was wired for a f150, and uses the 7 round light plug. It has electric brakes and every thing works great other than the truck doesn't know the trailer is connected when it's plugged in. I get the " trailer disconnected " warning in the dash when I apply the trailer brake on the dash.

All any idea ? What contact in the 7 round tells the truck that the trailer is there?

Thanks!

Bad fuse?

This trailer has electric brakes , no battery, so the charging fuse would not need to be installed, I was wondering what pin on the 7 tells the truck the trailer is connected?

When I use the manual brake on the TBC it displayed the warning and the trailer brakes don't work..

I'll double check all wires.

did you put the relay and fuse in under your hood?

No sir I didnt, from reading here and elsewhere that the fuse and relay was only there to charge the trailer breakaway battery , which mine does not have. Is it required to have those in to make the connection so the truck knows the trailer is back there?

yes. it makes all the lights work too.

My lights did work without it installed!

interesting. but that fuse and relay will make the brakes work

Ok I'll put them in, I just went out to the truck and got them out of the glove box. " Hey there made in USA"

What fuse slots do they go into ?

shit....... i cant remember off the top of my head. it is in the owners manual. it took me a while to find it, but it is there